Violence is in the air these days. It was visible to the world in Manchester, Birmingham and London in the days before the British general election June 8. It was visible on the baseball field in Alexandria, Virginia, on Wednesday morning as a Donald Trump hater and Bernie Sanders volunteer took a rifle and shot House Majority Whip Steve Scalise and four others while Republicans were practicing for Thursday’s congressional ballgame.

Violence is increasingly visible from or threatened by ski-masked, hammer-armed antifas — people employing fascist-style intimidation on those who disagree — on campuses from Berkeley to New England and in the streets of “cool cities” such as Portland. Contrary to mainstream media expectations, the violence and threats come almost entirely from the political left, not the right.

Sanders immediately issued a strong statement denouncing violence. That’s in character. He had also called for free speech on campus when Ann Coulter was barred from Berkeley, as did fellow left-wingers Elizabeth Warren and Maxine Waters. That’s in line with longtime liberal tradition yet contrary to the policies and actions of so many college and university administrators these days.

Unfortunately, it’s not hard to find left-wing tweets advocating violence against President Trump and Republicans. And the “arts” community contributes its share. Comedian Kathy Griffin posted a picture of herself holding a likeness of the bloody severed head of the president. In New York, Shakespeare in the Park’s staging of “Julius Caesar” features an orange-haired Caesar being stabbed to death by political rivals.

And there have been multiple violent threats and some actual instances of violence against Republican House members. Virginia’s Tom Garrett canceled town halls in response to a message that said, “This is how we’re going to kill your wife.” The message to upstate New York’s Claudia Tenney was, “One down, 216 to go.”

A Tucson school official was arrested for threatening that Arizona’s Martha McSally’s “days are numbered.” A woman was charged with felony reckless endangerment for trying to drive Tennessee’s David Kustoff’s car off the road.

Not all the violence has come from people on the left. Just before a May 25 special election, Montana Republican candidate Greg Gianforte body-slammed a reporter who was questioning him persistently. He won anyway and apologized at his victory party. Charged with assault, he was sentenced to 40 hours of community service and, unprompted, contributed $50,000 to the Committee to Protect Journalists, a worthy cause.

Some will say that this is a natural reaction to Trump’s offenses against propriety and the allegedly harmful policies he and congressional Republicans support. Certainly, Trump has repeatedly transgressed long-standing political etiquette, and in ways that often harm him and his party more than his opponents. His tweet about having tapes in the White House motivated James Comey, according to his own account, to leak information to The New York Times in the hope that it would prompt the appointment of a special prosecutor.

Which it did, even though regulations limit such appointments to criminal cases and the investigation of Russian involvement in our election is an intelligence investigation in which, as far as we know, there is no indication that anyone committed a crime.

Trump’s violations of political protocol have also sparked a political backlash. It hasn’t resulted in a Republican defeat yet in congressional special elections — all so far in districts Trump carried handily — but it could in the runoff next Tuesday for the seat representing Georgia’s 6th District.

That seat, in the northern Atlanta suburbs, is packed with affluent college graduates. Last year, it gave Trump only a 1.5 percentage-point edge, in contrast with the 20-point margins Republicans usually win there. Democratic candidate Jon Ossoff nearly won the seat by getting 48 percent of the vote in the April 18 all-party primary against multiple Republicans. He has led Republican Karen Handel by an average of 3 points in recent polling.

Even if Ossoff loses, a close race in such a district spells trouble for Republicans. It suggests that they can’t count on traditional margins — that they only can count on Trump’s much lower numbers — for such upscale seats. The good news for Republicans is that Democrats already hold most of these districts outside the South.

The political process provides avenues for those opposed to Trump or Republican policies. Too many Americans have convinced themselves that they are morally entitled to use violence to “resist,” as if Trump were some reincarnation of Adolf Hitler.